GPL license does not forbid commercial usage, but you should distinguish between commercial usage and commercial distribution (see next question).

If commercial usage does not involve distribution of ALGLIB code (or code which depends on ALGLIB), you can use ALGLIB without hesitation. However, ALGLIB Commercial Edition features a lot of improvements which are absent in Free Edition.

Almost surely - no. GPL license does not forbid commercial distribution explicitly, but it imposes several requirements that commercial users can't comply with.

The most important requirements are: a) you must distribute your program along with source code and under GPL, b) you can't restrict your users from copying your program, reselling copies or distributing them for free.

You can, but there is at least one reason to buy commercial license. Everything is OK while it is just running on your server. But any action connected with distribution - selling, sublicensing, transferring to someone under nondisclosure agreement - will trigger copyleft clause. So it is safer and more convenient to buy commercial license.

We offer you two payment methods. Plastic cards are the easiest and fastest way to pay. You should fill order form on ALGLIB website, then you get redirected to secure webform where you should enter your card number and other relevant information. Order will be processed within one business day after payment is done. Source files with your name in the "License information" section will be delivered to you by e-mail. In case you didn't get ALGLIB in time, please contact us.

Another payment method is bank transfer. It is slower (takes from 3 to 5 days) but sometimes can be more appropriate. You should fill order form on ALGLIB website, then within one business day an invoice will be issued. After paying an invoice you can either (A) wait for the money to enter our bank account - generally up to 3 days, or (B) send us confirmation of the payment (scanned copy of the bank documents, screenshot from internet banking system or accounting program). Then within one business day you will receive Commercial Edition of ALGLIB.

Yes. We offer you unconditional 90-day money back guarantee. If, within 90 days from payment, you will understand that for some reason you don't want to use ALGLIB anymore, you can contact us and we will return your payment back to you.

If money was paid by bank transfer, we will send them back to your account. In case payment by plastic card was used, we will refund your money back to your card.

First limitation is performance. Free Edition does not include multithreading functionality and low level optimizations. It is good on small and medium-scale computational problems, but may be too slow on large-scale ones.

Second limitation is license. GPL license, which is used by Free Edition of ALGLIB, is not good for most commercial applications.

No. First, about 20% of GPL'ed ALGLIB comes from several well-know open source projects (LAPACK and Cephes). Several contributions/patches were submitted by ALGLIB users. However, all such code was contributed under permissive licenses like BSD, so it is compatible with both open source and commercial licenses used by ALGLIB.

Second, Commercial Edition of ALGLIB includes Intel MKL - highly optimized numerical library which is used to accelerate ALGLIB on Intel CPU's. We obtained license from Intel Corporation which allows us to include MKL into ALGLIB.

We should note that section 7 of ALGLIB License Agreement (commercial one) explicitly states and warrants that we have right to license ALGLIB under commercial license.

Yes. You can freely distribute ALGLIB source under GPL terms (or use it under commercial license terms). But if you want to use ALGLIB name for something other than original ALGLIB distribution, you should ask our permission. You can read our trademark policy for more information.

AlgoPascal is a programming language developed for ALGLIB project. More than 95% of ALGLIB source is written in AlgoPascal and translated into C and C# by AlgoPascal translator. That is how we can simultaneously support C++ and C# versions of ALGLIB package - we support only one version of ALGLIB, which is written in AlgoPascal, and automatically translate it to C++ and C#.

X-generator is another tool developed exclusively for ALGLIB. It is a generator of wrappers for the C/C# computational cores. This generator is heavily used by Python and VB.NET releases of ALGLIB. It is also used to generate doctests - code snippets, which are used as both examples (doc) and test suite (tests).

Both technologies are kept private, but result we've got with these tools - ALGLIB - is freely available under GPL.